In a digital weigher, an analog weighing signal of objects which is detected by a weight sensor such as a load cell is converted into a digital weighing signal and control processes are performed using the digital weighing signal. The digital weighing signal contains oscillating components of an oscillation unique to the digital weigher, a oscillation due to external causes, etc. The oscillating components are removed by using a digital filter.
In the digital filter, to remove an oscillating component in which its frequency characteristic is varying with a passage of time, like the oscillation due to the external causes, etc., of the oscillating components contained in digital weighing signal, a frequency range of the oscillating component to be removed is changed by changing a transfer function according to the digital weighing signal input. As a method of changing the transfer function, there are a method of re-calculating a filter coefficient and a method of changing a filter order (the number of unit filters).
However, in the method of re-calculating the filter coefficient, an amount of repeated calculation is great and complex calculation is necessary, which will increase a calculation time. That is, if the filter coefficient is re-calculated during weighing of the objects, a time that passes until the digital weighing signal falls within a predetermined allowable damping range (time that passes until the digital weighing signal becomes a usable weight value of the objects) will increase.
As a solution to this problem, for example, Patent Literature 1 discloses a digital filter in which it is determined whether or not an amplitude of an oscillating component contained in a digital weighing signal derived by performing a wave filtering process by a filter means falls within a predetermined allowable damping range in every predetermined sampling of the digital weighing signal in one weighing cycle, and a filter order of the filter means is increased if it is determined that the amplitude of the oscillating component does not fall within the predetermined allowable damping range, thereby changing a frequency range of an oscillating component to be removed by the filter means. According to this digital filter, the oscillating component to be removed is changed by changing the filter order of the filter means depending on whether or not the amplitude of the oscillating component contained in the digital weighing signal derived by performing the wave filtering process falls within the predetermined allowable damping range. Therefore, an amount of calculation in the wave filtering process in the filter means can be reduced.